Add some thin wrappers around ocfs2_insert_extent() for each of the 3different btree types, ocfs2_inode_insert_extent(),ocfs2_xattr_value_insert_extent() and ocfs2_xattr_tree_insert_extent(). Thelast is for the xattr index btree, which will be used in a followup patch.All the old callers in file.c etc will call ocfs2_dinode_insert_extent(),while the other two handle the xattr issue. And the init of extent tree arehandled by these functions.

When storing xattr value which is too large, we will allocate some clustersfor it and here ocfs2_extent_list and ocfs2_extent_rec will also be used. Inorder to re-use the b-tree operation code, a new parameter named "private"is added into ocfs2_extent_tree and it is used to indicate the root ofocfs2_exent_list. The reason is that we can't deduce the root from thebuffer_head now. It may be in an inode, an ocfs2_xattr_block or even worse,in any place in an ocfs2_xattr_bucket.